The present invention relates to a process of biochemically converting heavy crude oils to upgraded light crude oils containing lighter hydrocarbon material, less organic sulfur and nitrogen and a reduced amount of trace metals. More specifically, the present invention provides a process of treating low grade heavy crude oils at atmospheric pressures and low to moderate temperatures with aerobic or anaerobic extremophilic microorganisms, which have been selected through nutritional stress by adapting them to elevated temperatures, pressures, salinity, elevated toxic metal concentrations and pH extremes.
Crude oil is removed from the earth as a comparatively volatile liquid composed primarily of hydrocarbons, with traces of sulfur, nitrogen or oxygen compounds, as well as trace amounts of metals. The elemental composition of petroleum varies greatly from one deposit to another. Carbon and hydrogen are the primary components, but other elements present include sulfur ranging from trace to 8.0% by weight, nitrogen from trace to 6% by weight, oxygen from trace to 1.8% by weight and trace amounts of other metals such as nickel and vanadium.
Heavy oils, residuum, and oil wastes represent a substantial resource if a low-cost technology for their processing could be developed. In terms of reserves, 50-70% of original oil is still in place and is available. However, it is heavy and requires extensive secondary and tertiary recovery technology. Similarly, wastes from oil processing amount to 400 million gallons annually within the U.S. alone.
Crude oils are the basic raw material for refineries. Hydrocarbons, organic sulfur, organic nitrogen and trace metals content of crude oils is used to classify them as heavy and light crude oils. For example, heavy crude oil has a high proportion of viscous, high-molecular weight hydrocarbons and often a high content of compounds containing organic sulfur, organic nitrogen, organic oxygen and trace metals. In contrast, light crude oil has a high proportion of low viscosity, low molecular weight hydrocarbons and a low content of compounds containing organic sulfur, organic nitrogen and trace metals. Consequently, when used as refinery feedstock, heavy crude oil requires more processing than the light crude in order to obtain the more salable, low molecular weight products. Moreover, high sulfur content crude oil is undesirable because it forms sulfur containing products such as sulfur containing gasoline, diesel and petroleum products which when used pollute the environment. As a result, additional processing is required to sweeten or desulfurize the finished gasoline or other stocks. Similarly, a high organic nitrogen and trace metal content is undesirable in crude oils because both organic nitrogen compounds and trace metals cause severe poisoning of catalysts required in the downstream processing of crude oil.
In the past, attempts have been made to reduce the content of sulfur, nitrogen and trace metals by numerous processes, either upstream or downstream of a given oil product, depending on the specifications of the finished product or other stocks. For example, mercaptans and hydrogen sulfide are removed by using regenerative solution processes. Hydrotreating of petroleum products is widely used to achieve desulfurization and eliminate other undesirable impurities such as nitrogen and oxygen. Problems associated with these processes include cost effectiveness and refinery wastes.
The use of thermophilic microorganisms to break down complex hydrocarbons in the laboratory environment, has been disclosed in the patent literature. For example, U.S. Pat. No. 2,413,278 to Zobell, discloses the use of bacteria from the genus Desulfovibrio. Some species of this bacteria are disclosed as being active in a temperature range from 70.degree. F. and 180.degree. F. (21.1.degree. C. to 82.4.degree. C.). These bacteria are strict anaerobes, and are inhibited by H.sup.+ ion concentrations lower than pH 6.0. Additionally, there is no disclosure that these microorganisms are functional at anything but ambient pressures. Similarly, in U.S. Pat. No. 2,660,550 to Updegraff et al., the same thermophilic bacteria described in the Zobell patent are used and molasses is introduced to the well water as a source of nutrients and minerals. As in Zobell, the bacteria, although described as highly thermophilic, were not tested for growth under high pressures, salinities and aerobic conditions.
Bacterium useful for cleaving C--S bonds for sulfur removal from dibenzothiophene to provide predominately inorganic sulfates and 2-hydroxybiphenyl is described in U.S. Pat. No. 5,002,888 to Kilbane, II. The preferred microorganism is identified as Bacillus sphaericus ATCC 53969. The '888 disclosure describes this bacteria as being able to metabolize the C--S bonds at temperatures from about 20.degree. C. to 34.degree. C. There is no teaching or suggestion that this microorganism and method can be used at high pressures and temperatures. Further, dibenzothiophene is one of the many sulfur containing compounds (&lt;1% of total organo sulfur content) present in crude oils whose chemical and biochemical reading varies with the chemical structure of a particular compound.
Generally, the art is substantially bereft of methods for upgrading heavy crude petroleum over a relatively short periods of time (from 24 hours to 50 hours) by contact with microorganism(s) which have been conditioned and adapted to survive and grow at elevated temperature, pressure, salinity, elevated toxic metal concentrations and pH extremes also known as extremophiles.
It would be desirable to provide such a process which overcomes this deficiency associated with the prior art. It is, therefore, an object of the present invention to provide a general process for upgrading a low grade heavy crude oil feedstock by lowering a high content of organic sulfur, organic nitrogen, oxygen and trace metal through the use of a biocatalyst(s).
It is another object of the present invention to upgrade heavy crude oil by using modified extremophilic bacteria to achieve the biochemical conversion of low grade heavy crude oils to upgraded higher quality feedstock.